Our goal is to develop objective electrophysiological tests of general cognitive capability in infants and children. Such tests are expected to be especially important in identifying the deficiencies responsible for the failure to learn, to communicate and to conceptualize. Our current experiments record long-latency waveforms of the event-related brain potential (ERP) to auditory and visual events delivering various kinds and amounts of information. Features of the ERP response (e.g., wave latencies, amplitudes, etc.) are being examined in search of criteria that will distinguish specific types of cognitive deficiencies. Our present measurements are focused upon the P3 wave (latency ca. 300-800 msec), the Nc wave (latency ca. 350-700 msec), and the Pc wave (latency ca. 900-14-- msec). These waves, which change considerably in amplitude and latency with maturation from infancy to adulthood, seem to reflect different sorts of cognitive processing.